Many electrophotographic developer roller coatings, including polyurethane/urea, silicones, polyester, and polyamides, are inherently quite resistive in nature. These developer roller coating, when used on certain soft rubber cores, such as epicholorohydrin (ECO) or ionically conductive urethane rubbers, exhibit lower resistivity than they inherently are. While not being limited to a theory, it is believed that this phenomenon is due to the physico-chemical interaction of the core rubber with the coating. This interaction results in a resistivity gradient through the thickness of the coating with highest resistivity closer to the outer surface of the coating. In addition, this gradient in resistivity can cause large fluctuations in overall coating resistivity due to coating thickness variation. This gradient in resistivity is also affected by process conditions, such as cure time, temperature, and aging. The variation in overall resistivity and the resistive thickness of the coating affects the precise functioning of the precise developer roll.
Hence, there is a clear need for modification of resistivity in the developer roll to help precisely control the toner development in electrophotography.